The present invention relates to a communication/exchange processing system and more particularly to a system for preventing a system-down phenomenon due to trouble with communication clocks used to perform data transmission/reception.
Generally, clocks can be divided into a process clock used to perform a work in a node and a communication clock used to transmit/receive data to/from another node. The process clock is generally a clock used in CPUs included in each node and is used by being generated through a crystal oscillator, etc. However, the communication clock relates to data transmission/reception, and its pulse width should be precisely controlled, as compared with the process clock. There are several devices for generating such a reference communication clock. A typical one is a standard communication clock generator comprising not only an oscillation circuit but also several stabilization circuits to stabilize the pulse width of clock output from the oscillation circuit, and the generator itself is constituted by a high precision control system. Accordingly, such a standard communication clock generator STD is very expensive as compared with an ordinary crystal oscillator. Due to this reason, all nodes constituting a network system generally do not have a standard communication clock generator STD but several nodes constitute a group so that each group generally has only one standard communication clock generator.
FIG. 1 shows the constitution of such a network, in which each group comprises several nodes.
In FIG. 1, when a node N 1 of nodes included in a group-1 comprises a standard communication clock generator STD, the other nodes (N2, N3, N4, N5, N6, N7 . . . ) included in the same group receive a standard communication clock from node N1 and generate a communication clock using a clock recovery circuit. Here, each node has the constitution as shown in FIG. 2.
With reference to FIG. 2, a node comprises a communication/exchange processing portion 201 and a subscriber processing portion 202. The communication/exchange processing portion 201 is a portion for performing a required operation when data is transmitted to or received from other nodes included in the network or received from other nodes and simultaneously performing an exchanger control of data which is transmitted and received through its node. Subscriber processing portion 202 is for user operating regions belonging to each node and has such a constitution as shown in FIG. 3. In FIG. 3, subscriber control portion 301 performs an entire control of subscriber processing portion 202, and comprises an analog line interface (ALI) for performing an interface with respect to analog type terminal equipments and a digital line interface (DLI) for performing an interface with respect to digital type terminal equipment. The ALI may be connected with analog telephone equipment 302, and the DLI may be connected with digital telephone equipment 303, facsimile equipment 304, monitor 305, printer 306, copier 307, . . . , etc.
Meanwhile, a conventional communication/exchange processing portion 201 is constructed as shown in FIGS. 4A and 4B, which comprises a multi-line interface means ML1, a switching module SWM, a communication processor CPM, a standard communication clock generator STD, a memory MEM and a clock module CKM, or comprises a multi-line interface means ML1, a switching module SWM, a communication processor CPM, a recovery communication clock generator RCV, memory MEM and clock module CKM. As the device for generating a reference communication clock, standard communication clock generator STD is used in FIG. 4A, and recovery communication clock generator RCV is used in FIG. 4B. The reference communication clock generated through the above apparatuses is supplied to clock module CKM to generate various application communication clocks used for communication operations. The switching module SWM is for performing a switching operation via software, one end of which is connected to the multi-line interface means ML1 and the subscriber processing portion while its other end is connected to the communication processor CPM and clock module CKM, etc., thereby performing a switching operation according to channels. For instance, if there are twelve logic channels per transmission line, assuming that a first channel is for transmitting and receiving a communication clock, a second to tenth channels are for transmitting and receiving data between the communication processors of the respective nodes, eleventh and twelfth channel are for transmitting and receiving data between communication processor CPM and subscriber processing portion, switching module SWM connects multi-line interface means ML1 to clock module CKM in the case of the first channel, to communication processor CPM in the case of the second to tenth channels, and connects communication processor CPM to subscriber processing portion 202 in the case of the eleventh and twelfth channels.
However, the data communication/exchange processing portion 201 having the above-described constitution does not have a measure for the prevention of clock trouble, thereby experiencing occurrences of the system-down phenomenon of communication/exchange processing portion 201, that is, to make communication with other nodes impossible. Also, as shown in FIG. 1, even if communication/exchange processing portion 201 is not down, communication is still impossible when all of the communication/exchange processing portions of adjacent nodes are down. Accordingly, the occurrence of the system-down phenomenon of communication/exchange processing portion 201, should be reduced wherever possible.